Field of Invention
The present invention relates generally to biotherapeutics directed at the inhibitory co-signaling receptor, BTLA and more specifically to therapeutic indications including autoimmune and inflammatory disorders.
Background Information
In healthy individuals the natural inflammatory response to infections and cancer is tightly regulated by a number of positive and negative control mechanisms on multiple cell lineages. This regulation can at times be co-opted by specific infectious agents or when specific pathways are compromised by somatic mutations leading to diseases of inflammatory pathogenesis. Activation of TNFRSF14 (Herpesvirus entry mediator, —HVEM) within various tissues by its ligands LIGHT (TNFSF14), BTLA (B and T Lymphocyte Attenuator), and CD160 leads to a broad range of inflammation countered by the activation of lymphocyte expressed BTLA by HVEM. CD160 shows more restricted cellular expression on natural killer cells and cytotoxic T cells and was reported to also inhibit lymphocytes responses. However, it has been determined that CD160 activates positive signals in lymphocytes in response to HVEM ligation.
Tumor necrosis factor inhibitors including the decoy receptor etanercept and antibodies (eg., adalimumab) have shown significant responses in patients with autoimmune diseases. TNF inhibitors are effective in 30-40% of patients with rheumatoid arthritis and other autoimmune diseases. However, a majority of patients show a partial or no response to this class of drugs. The basis of this failure to respond to TNF inhibitors remains unexplained. The mechanism of action of the TNF inhibitors is direct blockade of TNF binding to its receptors, halting a proinflammatory pathway. The main effect of blocking TNF is to quell innate inflammatory cells, but T cells may not be impacted, and TNF blockade alone may not reestablish homeostasis. The present invention targets a specific inhibitory pathway to attenuate inflammatory pathways and pathologic immune responses.
Substantial evidence indicates that HVEM is critically important when expressed in mucosal epithelium to suppress inflammation mediated by autoreactive T cells and macrophages. In a mouse model of Crohn's Disease, the loss of TNFSF14 in epithelium dramatically accelerated the onset of intestinal inflammation; BTLA expression in T cells and innate effector cells was required to suppress inflammation. These results established the physiological relevance of the HVEM-BTLA signaling pathway between different organs. In a chronic lung inflammation model of asthma, the LIGHT-HVEM system revealed itself as an essential pathway for memory T cells that drive pathology to persist in the lung. Moreover, LIGHT-LTβR pathway drives pathologic lung remodeling. These attributes place the HVEM system in a unique position to regulate immune responses. While the use of biologic intervention to target these pathways has led to some success in controlling HVEM mediated inflammation, it has previously been difficult to discriminate tissue and cell-specific effects due to the complexity of ligand interactions and the variability in response from specific targets.
Inflammatory responses to infections and cancer are regulated by a number of positive and negative control mechanisms on multiple cell lineages. Natural killer (NK) cells are an essential component of the innate immune system that protect against a wide range of pathogens, particularly against herpesviruses. Mature NK cells express a diverse array of receptors that activate cytolysis and cytokine release. NK cell activation is balanced by an equally varied number of inhibitory receptors that prevent uncontrolled cytolysis and inflammation through the recognition of self major histocompatibility complex (MHC) molecules in healthy, uninfected cells.
Many herpesviruses have manipulated this balance in order to prevent clearance of infected cells, allowing for viral replication and the establishment of latency. In order to become fully functional effector cells receptive to activating ligands, NK cells develop and are primed in response to the cytokine IL-15, and to a lesser extent IL-2 in vivo, both of which activate common γ chain signaling. IL-2 and IL-15 also induce the expression of antiviral interferon-γ and surface lymphotoxin (LT)-αβ.
Recent studies have shown that somatic mutations in TNFRSF14 either through deletion or nonsysnonymous mutation are among the most common gene alterations in follicular and diffuse large B cell lymphoma. Follicular lymphoma harboring acquired TNFRSF14 mutations are associated with worse prognosis, highlighting the anti-inflammatory effect of HVEM in the tumor microenvironment. While the mechanism for the tumor suppressive role of HVEM is unclear, the absence of NK cell and cytotoxic T cell costimulation through CD160 may lead to aborted anti-tumor responses. Alternatively, the absence of HVEM would prevent inhibition of T cells expressing BTLA, thus promoting the release of B cell growth factors. Finally, the absence of HVEM may act in a cell intrinsic manner in tumor cells to prevent the initiation of death signals. Additionally, lymphoma bearing HVEM deletions would express BTLA alone and not in a complex with HVEM, and thus would be exposed to ligands from other cells, antibodies or biologics which could drive inhibitory signals to the tumor cell.
The HVEM (TNFRSF14) (EMBL-CDS: AAQ89238.1: Homo sapiens (human) HVEM is a member of the tumor necrosis factor receptor superfamily expressed on lymphocytes, regulates immune responses by activating both proinflammatory and inhibitory signaling pathways (alternatively, one of skill in the art can use other known HVEM sequences, such as (Genentech) or the NCBI sequence, which may differ by 1 base (e.g., a Lys to Arg change at position 16 in the signal sequence (not in the mature protein)). HVEM binds the TNF-related ligands LIGHT (TNFSF14) and LT-α, and the immunoglobulin domain containing receptors B and T lymphocyte attenuator (BTLA). BTLA activation results in phosphorylation of its cytoplasmic tyrosines and recruitment of the tyrosine phosphatases Src homology domain 2 containing phosphatase-1 (SHP1) and 2, resulting in diminished antigen receptor signaling in T cells and B cells. In contrast, CD160 both activates NK cells and acts as an inhibitory receptor on a subset of CD4+ T cells. In T cells, LIGHT-HVEM signaling enhances antigen induced T cell proliferation and cytokine production.
Human Cytomegalovirus (CMV), a β-herpesvirus, contains a number of genes that modulate host immune responses and specifically NK cell activation. Many of these genes are encoded within the unique long subregion (UL)/b′ of the CMV genome that is not essential for replication in vitro The UL144 open reading frame contained within the (UL)/b′ locus was first identified as an expressed transcript encoding a type 1 transmembrane protein and as an ortholog to HVEM. UL144 does not bind LIGHT or LT-α, presumably because it lacks the third and fourth cysteine-rich domains (CRD) contained in HVEM, although it does bind and activate BTLA via CRD1 to restrain T cell proliferation.
Because HVEM activates both proinflammatory and inhibitory signaling pathways, HVEM has an important role in regulating inflammation. Additional evidence supports the importance of HVEM's role. For example, HVEM plays a role in suppression of inflammation mediated by autoractive T cells and macrophages in mucosal epithelium. In a mouse model of Crohn's disease, the loss of HVEM in epithelium dramatically accelerated the onset of intestinal inflammation; BTLA expression in T cells and innate effector cells was required to suppress inflammation. In a chronic lung inflammation model of asthma, the LIGHT-HVEM system is an essential pathway for memory T cells that drive pathology in the lung. Moreover, the LIGHT-LTβR pathway drives pathologic lung remodeling and the HVEM-BTLA system can counteregulate the LTβR pathway.
A ligand-specific HVEM protein, including a ligand-specific HVEM protein that binds to BTLA but not to LIGHT or CD160, would be useful for treating inflammatory diseases and may also be useful for suppressing growth of BTLA expressing tumor cells. An HVEM specific for CD160 may provide activating signals that induce innate lymphocytes, such as NK cells, or T cells to arrest the growth or kill tumor cells.